The main problem might be actually in your bet sizes and he could easily see weakness in them and that's as well the reason why he decided to shove. I would likely consider betting the flop bigger and as well a bit bigger on turn.

Turn bet is mainly as well for free showdown and not having a huge guess on river either to Call or not if he bets.

As you said yourself he is a 100% range player. And therefore if he really had the 8x then he wouldn't shove directly but rather slowplay. And as you went for value preflop then I would Call his shove.

Flop - I bet (big ) , he calls , turn K: he checks , what do I do ?

You would have been committed anyways then if you would have made bigger bets and turn is almost all-in anyways. So therefore I'd just bet the turn as well for value from any kind of weaker PPs/pairs.

And actually it seems that your 3bet size is a bit too big as well. I might do it a bit smaller while we even have position on him, ~$1,50.